Magnetic field sensor

ABSTRACT

In one aspect, a magnetic field sensor includes a chopper stabilized amplifier and a plurality of Hall-type elements in parallel and connected to the chopper stabilized amplifier. In another aspect, a magnetic field sensor includes a chopper stabilized amplifier and a plurality of Hall quad elements in parallel and connected to the chopper stabilized amplifier. In a further aspect, a current sensor has a bandwidth of 1 MHz and includes a chopper stabilized amplifier and a plurality of Hall quad elements, fabricated in silicon, in parallel and connected to the chopper stabilized amplifier.

BACKGROUND

Various types of magnetic field sensing elements are known, includingHall effect elements and magnetoresistance elements. Magnetic fieldsensors generally include a magnetic field sensing element and otherelectronic components. Some magnetic field sensors also include a fixedpermanent magnet.

Magnetic field sensors provide an electrical signal representative of asensed magnetic field, or, in some embodiments, fluctuations of themagnetic field associated with the magnet. In the presence of a movingferromagnetic object, the magnetic field signal sensed by the magneticfield sensor varies in accordance with a shape or profile of the movingferromagnetic object.

Magnetic field sensors are often used to detect movement of features ofa ferromagnetic gear, such a gear tooth and/or gear slots. A magneticfield sensor in this application is commonly referred to as a “geartooth” sensor.

In some arrangements, the gear is placed upon a target object, forexample, a camshaft in an engine, thus it is the rotation of the targetobject (e.g., camshaft) that is sensed by detection of the movingfeatures of the gear. Gear tooth sensors are used, for example, inautomotive applications to provide information to an engine controlprocessor for ignition timing control, fuel management, wheel speed andother operations.

SUMMARY

In one aspect, a magnetic field sensor includes a chopper stabilizedamplifier and a plurality of Hall-type elements in parallel andconnected to the chopper stabilized amplifier. In another aspect, amagnetic field sensor includes a chopper stabilized amplifier and aplurality of Hall quad elements in parallel and connected to the chopperstabilized amplifier. In a further aspect, a current sensor has abandwidth of 1 MHz and includes a chopper stabilized amplifier and aplurality of Hall quad elements, fabricated in silicon, in parallel andconnected to the chopper stabilized amplifier.

DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a circuit diagram of an example of a Hall effect element;

FIG. 2 is a circuit diagram of an example of a Hall quad element;

FIG. 3 is block diagram of an example of a magnetic field sensor;

FIG. 4 is block diagram of another example of a magnetic field sensor;

FIG. 5 is a block diagram of a dual Hall element;

FIG. 6 is a block diagram of two dual Hall elements;

FIG. 7 is a block diagram of a octal Hall element; and

FIG. 8 is a block diagram of different configurations of the octal Hallelement.

DETAIL DESCRIPTION

Described herein are techniques to fabricate a magnetic field sensor. Inone example, the techniques described herein are used to reduce the timeconstant of a Hall effect sensor, which allows for a Hall amplifier tobe chopped. Typically, one chops the Hall plate by varying the power andsignal leads in order to place the Hall offset at a higher frequency,where it can be filtered out. However, as described herein, a pluralityof Hall quad elements in parallel reduces the offset which then can betrimmed out. The techniques described herein result in a low offsetsolution with higher bandwidth than other standard Hall choppingsolutions, which enables higher bandwidth sensing with minimal increasein offset drift over temperature and stress. In one particular example,the bandwidth of a silicon-based device (e.g., a current sensor) usingthe techniques described herein increases from about 250 kHz to 1 MHzbecause chopping may now be performed at about 8 MHz or 10 MHz toeliminate offsets.

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element may be a single element or,alternatively, may include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element may be a device made ofa type IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) andvertical Hall elements tend to have axes of sensitivity parallel to asubstrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

Referring to FIG. 1, in one example, a Hall effect element 100 includesa single Hall plate 102. The Hall plate 102 is connected to a voltagesource, V_(HallRef), at a first contact 106 a and the Hall plate 102 isconnected to ground at a second contact 106 b to generate a current,I_(Hall), that flows through the Hall plate 102 (i.e., current flowsfrom the first contact 106 a to the second contact 106 b). Theresistance of the Hall plate 102 is R_(Hall). In other examples, thecontact 106 a is connected to a current source that generates thecurrent, I_(Hall).

When the Hall plate 102 is exposed to a magnetic field a voltage,V_(Hall) _(_) _(P), is generated at a third contact 106 c and a voltage,V_(Hall) _(_) _(N), is generated at the fourth contact 106 d to producean output voltage of the single Hall plate 102 equal to V_(out) orV_(Hall) _(_) _(P)−V_(Hall) _(_) _(N). In one example, the Hall plate102 is a rectangular-shaped plate. In one particular example, the Hallplate 102 is a square-shaped plate. In a further example, the Hall plateis a cross-shaped plate. Referring to FIG. 2, sometimes single Hallplates have DC offsets (sometimes referred to herein as Hall offsets).That is, with a zero magnetic field, V_(out) is nonzero. The offset mayalso change with temperature or stress. To eliminate these DC offsets,it is common to use four single Hall plates each rotated in quadrature(e.g., each Hall plate is rotated at least 90° from each other) to forma Hall quad element.

In one example, a Hall quad element 202 includes Hall plates 102 a-102d. Each of the Hall plates 102 a-102 d are substantially the same inshape, size and functionality. The Hall quad element 202 has a firstoutput terminal 204 a and a second output terminal 204 b.

The Hall plate 102 a includes a first contact 206 a, a second contact206 b, a third contact 206 c and a fourth contact 206 d. The Hall plate102 b includes a first contact 216 a, a second contact 216 b, a thirdcontact 216 c and a fourth contact 216 d. The Hall plate 102 c includesa first contact 226 a, a second contact 226 b, a third contact 226 c anda fourth contact 226 d. The Hall plate 102 d includes a first contact236 a, a second contact 236 b, a third contact 236 c and a fourthcontact 236 d.

A voltage source, V_(HallRef), is connected to the outermost corners ofthe plates 102 a-102 d. That is, the voltage source, V_(HallRef), isconnected to the first contact 206 a of the plate 102 a, the firstcontact 216 a of the plate 102 b, the first contact 226 a of the plate102 c and the first contact 236 a of the plate 102 d.

The ground is tied to the innermost corners of the plates 102 a-102 d.That is, the ground is connected to the second contact 206 b of theplate 102 a, the second contact 216 b of the plate 102 b, the secondcontact 226 b of the plate 102 c and the second contact 236 b of theplate 102 d.

When the Hall quad element 202 is exposed to a magnetic field a voltage,V_(Hall) _(_) _(P), is generated at the third contact of each of theplates 102 a-102 d. The third contacts of each of the plates 102 a-102 dare connected to the first output terminal 204 a. That is, the firstoutput terminal 204 a is connected to the third contact 206 c of theplate 102 a, the third contact 216 c of the plate 102 b, the thirdcontact 226 c of the plate 102 c and the third contact 236 c of theplate 102 d. The voltage at the first output terminal is equal toV_(Hall) _(_) _(P).

When the Hall quad element 202 is exposed to a magnetic field a voltage,V_(Hall) _(_) _(N), is also generated at the fourth contact of each ofthe plates 102 a-102 d. The fourth contacts of each of the plates 102a-102 d are connected to the second output terminal 204 b. That is, thesecond output terminal 204 b is connected to the fourth contact 206 d ofthe plate 102 a, the fourth contact 216 d of the plate 102 b, the fourthcontact 226 d of the plate 102 c and the fourth contact 236 d of theplate 102 d. The voltage at the second output terminal is equal toV_(Hall) _(_) _(N).

The voltage output of the Hall quad element 202 is equal to V_(Hall)_(_) _(P)−V_(Hall) _(_) _(N). The resistance of the Hall quad element202 is equal to R_(HallQuad)=R_(Hall)/4.

Referring to FIG. 3, a magnetic field sensor 300 (e.g., a Hall effectcurrent sensor) includes Hall quad elements in parallel (e.g., Hall quadelement 202 a, . . . , a Hall quad element 202N) and a chopperstabilized amplifier 304. The chopper stabilized amplifier 304 includesa first input terminal 332 and a second input terminal 334. The chopperstabilized amplifier 304 also includes a switch 322, a front end Hallamplifier 324 and a switch 326.

The Hall quad element 202 a includes a first output terminal 312 a and asecond output terminal 314 a and the Hall quad element 202N includes afirst output terminal 312N and a second output terminal 314N. Whenexposed to a magnetic field the first output terminals (312 a-312N) havea voltage, V_(Hall) _(_) _(P), and the second output terminals have avoltage, V_(Hall) _(_) _(N). The first output terminals (312 a-312N) areconnected together to the input terminal 332 of the chopper stabilizedamplifier 304 and the second output terminals (314 a-314N) are connectedto the second input terminal 334 of the chopper stabilized amplifier304.

By placing the Hall quad elements 202 a-202N in parallel, the combinedHall offset (the net offset of all the Hall quad elements) is furtherreduced. Putting the Hall quad elements 202 a-202N in parallel alsoallows for keeping the quad Hall plate symmetry for each Hall quadelement. The advantage of a quad Hall plate is that it cancels outstress induced offsets. This leaves just the construction based offsets(misalignment of contacts, and so forth . . . ) to trim out. Chopping asingle Hall plate removes both sources of offset. If chopping is notused, it is important to use quad Hall plates, as stress based offsetscan be unpredictable over temperature and lifetime. By getting rid ofthose, then just construction based offsets are trimmed out, which willbe relatively consistent or predictable over temperature and lifetime.

With a lower Hall resistance and higher Hall capacitance, the front endamplifier 324 can be chopped at a high frequency. This is based on thesettling time of the total Hall plate resistance and the parallelcombination of the Hall capacitance and input capacitance of the frontend Hall amplifier 324, as well as the ratio of the amplifiercapacitance to the Hall capacitance. Otherwise, the offset of the frontend Hall amplifier 324 could dominate the offset of the system.

As will be described further herein, one can asymptotically approach thenative Hall quad element time constant (R_(HallQuad)*C_(HallQuad)),which is the minimum limit, but the effect of the input capacitance ofthe amplifier, C_(InAmp), is reduced by the increase in the number ofHall quad elements.

The voltage received by the front end Hall amplifier 324 is equal to

${V_{InAmp} = {\left( {V_{{Hall}\_ P} - V_{{Hall}\_ N}} \right)*\left( {1 - e^{\frac{t}{\;^{R_{{{Hall}\_{Total}}*{({C_{inAmp} + C_{HallTotal}})}}}}}} \right)}},{where}$$R_{HallTotal} = {\frac{1}{N}*R_{{HallQuad},}}$C_(HallTotal) = N * C_(HallQuad)and the time constant is equal to:

${{R_{HallTotal}*\left( {C_{InAmp} + C_{HallTotal}} \right)} = {{R_{HallQuad}*C_{HallQuad}} + {\frac{1}{N}*R_{HallQuad}*C_{InAmp}}}},$where N is equal to the number of Hall quad elements, C_(InAmp) is theinput capacitance of the front end Hall amplifier 324, C_(HallTotal) isthe capacitance of the Hall quad elements and R_(HallTotal) is theresistance of the Hall quad elements so that adding Hall quad elementsin parallel reduces the time constant R*C towards being equal toR_(HallQuad)*C_(HallQuad) (i.e., as N gets larger). At the same time,the ratio of the Hall quad capacitance. C_(QuadTotal), to the inputcapacitance, C_(InAmp), goes up. When the front end amplifier 324 ischopped, the charge on the input capacitor goes into the Hallcapacitance, C_(HallTotal), causing a voltage step that has to settleout at the time constant above. As the ratio of capacitances increases,the step voltage decreases, meaning one does not have to wait as longfor the error to go below the desired accuracy. This means one can chopat a higher frequency than what the raw Hall plate can be chopped at,leading to a faster bandwidth part. Also, at the extreme, as describedherein, the voltage step is so small that the chopping frequency isactually limited by something else in the circuitry and not the accuracyof this settling from chopping.

In one particular example, the time constant is about 5 ns, whereR_(HallQuad) has an effective source resistance of about 4.4 kohm andC_(HallQuad) is about 0.8 pF and C_(InAmp) is about 1.1 pF.

In one particular example, three Hall quad elements are disposed inparallel and inside a conduction loop (e.g., conduction loop in FIG. 4)of a current sensor in order to get the best signal to noise ratio. Thefront end Hall amplifier 324 would then be chopped in order to get ridof the offsets in the front end Hall amplifier 324.

In another example, epitaxial resistors are disposed in parallel withthe Hall quad elements in order to reduce the offsets and time constant.However, there is a trade-off between area and signal to noise. That is,using epitaxial resistors occupy a smaller area, but the signal-to-noiseis worse.

Referring to FIG. 4, in another embodiment, a magnetic field sensor 300(e.g., a Hall effect current sensor) may include parallel Hall quadelements (e.g., a Hall quad element 402 a, a Hall quad element 402 b, aHall quad element 402 c and a Hall quad element 402 d). The Hall quadelements 402 a-402 d include a first contact 412 a-412 d and secondcontact 414 a-414 d, respectively. When exposed to a magnetic field(e.g., a magnetic field 418), the first contacts 412 a-412 d have avoltage, V_(Hall) _(_) _(P) and the second contacts 414 a-414 d have avoltage, V_(Hall) _(_) _(N). In this configuration an even number ofHall quad elements are disposed on opposite sides of a currentconduction loop 410. For example, Hall quad elements 402 a, 402 b are onopposite sides of a conduction loop 410 than the Hall quad elements 402c, 402 d. This configuration enables detection of the magnetic field 418generated in the conduction loop 410 by the current flow 408 and cancelsany external field by connecting the Hall quad elements 402 c, 402 d onopposite sides of the current loop 410 in opposite polarity. That is,the first output terminals 412 a, 412 b of the Hall quad elements 402 a,402 b are connected to the second output terminals 414 c, 414 d of theHall quad elements 402 c, 402 d and the second output terminals 414 a,414 b of the Hall quad elements 402 a, 402 b are connected to the firstoutput terminals 412 c, 412 d of the Hall quad elements 402 c, 402 d.Even though FIG. 4 depicts two Hall quad elements on each side of theloop 410, one of ordinary skill in the art would recognize that thenumber of Hall quad elements on each side is not limited to two.

One of ordinary skill in the art would recognize that the techniquesdescribed herein are not limited to Hall quad elements; but rather, theHall quad elements may be replaced by other Hall-type elements. Forexample, a Hall dual element 500 (FIG. 5) may be used. In otherembodiments, two dual elements 600 may be used (FIG. 6). In stillfurther embodiments a Hall octal element 700 may be used (FIG. 7). Asshown in FIG. 8, using a Hall octal element, the Hall voltage ismeasured eight times, one for each configuration 800 a-800 g. Forexample, in the configuration 800 a, current flows from contact 806a-806 b and the Hall voltage is measured between contacts 806 c-806 d.When extended to the remaining configurations 800 b-800 g stress orother effects on the die are averaged out. In other embodiments, othereven-sided Hall-type elements than the 4-sided (Hall quad element) and8-sided (Hall octal element) may be used such as 6-sided, 10-sided,12-sided and so forth. Though not as preferred as even-sided Hall-typeelements, odd-sided Hall-type elements may also be used. In stillfurther embodiments, another Hall-type element that may be used is acircular vertical Hall.

Elements of different embodiments described herein may be combined toform other embodiments not specifically set forth above. Variouselements, which are described in the context of a single embodiment, mayalso be provided separately or in any suitable subcombination. Otherembodiments not specifically described herein are also within the scopeof the following claims.

What is claimed is:
 1. A magnetic field sensor comprising: a chopperstabilized amplifier; and a plurality of at least three Hall-typeelements electrically connected in parallel to each other andelectrically connected to the chopper stabilized amplifier, wherein theplurality of at least three Hall-type elements ace a plurality of atleast four Hall-type elements disposed in a configuration to include anequal number of at least two Hall-type elements disposed on each side ofa U-shaped conduction loop, wherein the at least two Hall-type elementsdisposed inside the U-shaped conduction loop are disposed in an oppositepolarity than the at least two Hall-type elements disposed outside theU-shaped conduction loop.
 2. The sensor of claim 1 wherein the pluralityof at least three Hall-type elements comprises at least one of a Hallquad element, a Hall dual element or a Hall octal element.
 3. The sensorof claim 1, wherein the plurality of at least three Hall-type elementsare fabricated in silicon, and wherein the bandwidth of the sensor is 1MHz.
 4. A magnetic field sensor comprising: a chopper stabilizedamplifier; and a plurality of at least three Hall quad elementselectrically connected in parallel to each other and electricallyconnected to the chopper stabilized amplifier, wherein the plurality ofat least three Hall quad elements are a plurality of at least four Hallquad elements disposed in a configuration to include an equal number ofat least two Hall quad elements on each side of a U-shaped conductionloop, wherein the at least two Hall quad elements disposed inside theU-shaped conduction loop are disposed in an opposite polarity than theat least two Hall quad elements disposed outside the U-shaped conductionloop.
 5. The sensor of claim 4, wherein a Hall quad element of theplurality of at least three Hall quad elements comprises arectangular-shaped Hall plate.
 6. The sensor of claim 5, wherein theHall quad element comprises a square-shaped Hall plate.
 7. The sensor ofclaim 4, wherein a Hall quad element of the plurality of at least threeHall quad elements comprises a cross-shaped Hall plate.
 8. The sensor ofclaim 4, wherein a Hall quad element of the plurality of at least threeHall quad elements comprises four Hall plates of substantially similarshape.
 9. The sensor of claim 4, wherein the plurality of at least threeHall quad elements are fabricated in silicon.
 10. The sensor of claim 9,wherein a bandwidth of the sensor is 1 MHz.
 11. The sensor of claim 4,wherein the sensor is a current sensor.
 12. The sensor of claim 4,wherein a resistance of a Hall quad element of the plurality of at leastthree Hall quad elements is about 4.4 kohm and a capacitance of the Hallquad element is about 0.8 pF, and wherein an input capacitance of thechopper stabilized amplifier is about 1.1 pF.
 13. A current sensorcomprising: a chopper stabilized amplifier; and a plurality of at leastthree Hall quad elements electrically connected in parallel to eachother and electrically connected to the chopper stabilized amplifier,the plurality of Hall quad elements fabricated in silicon, wherein thecurrent sensor has a bandwidth of 1 MHz, wherein the plurality of atleast three Hall quad elements are a plurality of at least four Hallquad elements disposed in a configuration to include an equal number ofat least two Hall quad elements disposed on each side of a U-shapedconduction loop, wherein the at least two Hall quad elements disposedinside the U-shaped conduction loop are disposed in an opposite polaritythan the at least two Hall quad elements disposed outside the U-shapedconduction loop.
 14. The current sensor of claim 13, wherein a Hall quadelement of the at least three Hall quad elements comprises asquare-shaped Hall plate.
 15. The current sensor of claim 13, wherein aHall quad element of the at least three Hall quad elements comprises across-shaped Hall plate.
 16. The current sensor of claim 13, wherein aHall quad element of the at least three Hall quad elements comprisesfour Hall plates of substantially similar shape.
 17. The current sensorof claim 13, wherein a resistance of a Hall quad element of the at leastthree Hall quad elements is about 4.4 kohm and a capacitance of the Hallquad element is about 0.8 pF, and wherein an input capacitance of thechopper stabilized amplifier is about 1.1 pF.